This invention relates to a flexible joint for connecting two pipes, and in particular to a hollow flexible joint for connecting two rigid pipes in an engine exhaust system.
In for instance a conventional OHV engine, when the exhaust valve opens at the end of the expansion stroke, pressure in the cylinder is still considerably greater than atmospheric. If the exhaust port is allowed to discharge directly into atmosphere, the noise is comparable to that of the gases from behind a bullet in a pistol. Whilst in a multi-cylinder engine the noise can be considerably reduced by discharging all the exhaust pipes into a single branched pipe (manifold) so that the exhaust flow is smoother and more continuous, the noise level still exceeds acceptable levels. The exhaust gases are therefor required to be passed through an exhaust system including a silencer before escaping to atmosphere. Silencing inevitably leads to some loss of engine power because any restriction in escape of the exhaust gases also tends to reduce the amount of fresh charge entering the cylinder. Thus exhaust systems are designs of considerable complexity;; in recent U.K litigation, a major vehicle manufacturer indicated that a successful exhaust system for a new car took six months or more to design.
An engine creates torque, which is reacted by its mounting. To limit damage to the mounting, it is usual to interpose resilient support members between the engine and the mounting, which clearly then permit some movement of the engine. These self-induced engine movements are added to if the engine is a vehicle engine subject also to road vibrations, particularly if the engine is transversely-mounted.
In one known arrangement, currently in use on a small car, and sometimes known as a non-split exhaust system, the exhaust system is rigidly connected to the engine and moves with it; since however the exhaust system is mounted in cantilever and is of a length exceeding 1.5 meters, the system frequently breaks off adjacent the engine connection. In a second used arrangement, the exhaust pipe has a flattened section which acts as a hinge, the rear pipe section being secured to the vehicle chassis and with the front pipe section connected to hingedly-follow the engine movements; but there are frequently early failures due to metal fatigue on the flattened section. In another used arrangement, with a split-exhaust system, the engine and exhaust systems are connected by a flexible pipe comprised of overlapping helically-wound metal strip, which severs and/or separates and then is not gas tight.
There have been a number of prior proposals from the vehicle manufacturers aimed at preventing the engine movements damaging the exhaust system.
Thus Daimler-Benz DOS1526557 showed a pipe connector having spaced part-spherical ends resiliently-biased and/or clamped against mating pipe-ends; but relative lateral pipe end movement increases the distance between the mating parts so that the part-spherical ends either separate from the mating parts or the pipe ends are pulled inwards and the pipes stressed. A subsequent arrangement is that of DE3116290 in which the exhaust pipe and connecting section have overlapping curved flanges. which are clamped in the radial and axial directions by V-shaped clip.
Volkswagenwerk AG have proposed in U.S. Pat. No. 4,223,922 a pipe connection using a spherical sealing surface on one pipe which projects into an axial accommodating space of a mating pipe. In U.S. Pat. No. 4,289,169 an arrangement for multi-passage pipes (that is pipes which have exhaust channels separated from one another to improve the engine performance) is disclosed, also with a spherical mounting. In DOS2353914 a transversely-disposed leaf spring holds the surfaces together. Other disclosures are DOS2716894; DOS2623520; and U.S. Pat. No. 4,181,332.
Chrysler France have proposed in French Publication No. No. 2346631 cooperating male and female connectors, each with deformed spherical ends and so able to articulate, with the connection assured by a resilient coupling; a common resilient couping is shown for twin exhaust systems.
Regie Nationale des Usines Renault in U.S. Pat. No. 4,408,785 show a system for filtering vibrations from an internal combustion engine towards an exhaust pipe. The pipe ends are linked by an internal cylindrical element which is intended to ensure the pipe's continuity with a minimum or charge losses as well as passing along longitudinal compression stress.